1. Field of the Invention
The present invention relates generally to an improved safety mechanism for a fastener driving tool and more particularly to a new and improved safety mechanism having two interlock modes to prevent the inadvertent or accidental actuation of the fastener driving tool.
2. Background of the Invention
Portable fastener driving tools have enjoyed immense popularity in light manufacturing sectors for the last four decades. In their normal mode of operation, a fastener driving tool is actuated by air pressure so that a fastener, such as a nail, staple or the like, is ejected into a workpiece during a driving stroke of the tool. The exceedingly high air pressures used, on the order of 100 pounds per square inch, results in the fastener being ejected at a hiqh velocity.
Consequently, the operation of such a portable, hand-held fastener tool can be hazardous if they are not properly used. Attempts at eliminating accidental or inadvertent firing of the tool and personal injuries caused by the tools have been marginally successful. However, the safety mechanisms employed can be overcome. A common safety feature used in such tools includes a workpiece contact tip or nosepiece which, if not depressed, keeps the tool from firing. An efficiency feature of this safety configuration is that as long as the operator keeps the trigger depressed, the operator can continue firing fasteners with successive bumps of the contact tip against the workpiece.
Examples of designs incorporating safety features or mechanisms are disclosed in U.S. Pat. No. 3,784,077 issued on Jan. 8, 1974 and U.S. Pat. No. 4,260,092 issued on Apr. 7, 1981. The safety features disclosed in those patents tend to prohibit the disclosed fastener driving tool from firing if the nosepiece is not depressed first or if the nosepiece is not continually depressed. However, the trigger in these devices may be pivoted or depressed without the nosepiece also being depressed, thereby creating the possibility of accidental firing if the safety features of the nosepiece configuration are compromised through wear or mishandling.
Some prior tools also allow for continued actuation of the tool when the nosepiece only partially returns toward its inactivated, fully extended position, as for example upon recoil after the tool is activated. This causes the tool to recycle and creates the possibility that a fastener inadvertently will be driven, perhaps on top of a previously driven fastener.
A need exists for a safety feature that will not only prevent the trigger from being depressed when the nosepiece is not placed against a workpiece, but also renders the fastener driving tool inactive when the nosepiece is only partially relaxed.